Bonjour Jennifer !
With moments of the day, you will usually use only the definite article "l'/le/la" to express a general statement:
"Le soir, je me couche tard." (In the evening, I go to bed late.)
"L'après-midi, il fait la sieste." (In the afternoon, he has a nap.)
"La nuit, nous dormons." (At night, we sleep.)
See also our lesson on days of the week:
Using le with days of the week + weekend
I hope that's helpful!
À bientôt !